1. Field of the Invention
This invention concerns a lens apparatus for forming a object image on an image pickup element and particularly concerns the positioning of a motor, incorporated in a lens apparatus, etc.
2. Description of the Related Art
Conventionally, collapsible lens apparatuses, with which the total lens apparatus length is made variable between a usage state, wherein a plurality of image taking lenses are positioned at desirable lens intervals during image taking, and a housed state, wherein the lens intervals and interval with respect to an image pickup plane are narrowed, have been used popularly in digital still cameras, etc.
The varying of the total lens apparatus length is carried out by means of cams, helicoids, and other moving mechanisms to set the lens apparatus to an appropriate configuration. A zoom lens apparatus can also be arranged, with which the focal length is varied by driving a plurality of lens units separately.
FIGS. 11 and 12 are sectional views including the optical axis of a conventional lens apparatus, with FIG. 11 showing the state of the lens apparatus in the non-image-taking state, in which the lens apparatus is housed in a housing region of a main body of camera. FIG. 12 shows the state of the lens apparatus during an image taking, wherein the lens apparatus is driven from the housing region to an image taking region.
In FIGS. 11 and 12, Reference Numeral 101 denotes an image pickup element. The image pickup element 101 is a CCD, with 101a being an image pickup plane and 101b being a protective glass. Reference Numeral 102 denotes a CCD mounting base plate, which holds the image pickup element 101 and holds the respective parts that make up the lens apparatus to be described later. Reference Numeral 103 denotes an optical LPF (low pass filter), which makes use of the birefringence effect of quartz to repress the occurrence of luminance moiré and false colors. Reference Numeral 104 denotes a first lens unit that forms the optical system of the lens apparatus. Reference Numeral 105 denotes likewise a second lens unit and Reference Numeral 106 denotes a third lens unit.
Reference Numeral 107 denotes a fixed barrel with a substantially cylindrical shape that is fixed to the CCD mounting base plate 102. Reference Numeral 108 denotes a cam barrel with substantially cylindrical shape. On the outer peripheral surface of the cam barrel 108, a protrusion that serves as a cam follower is formed. A cam is formed on the inner peripheral surface of the fixed barrel 107, and engages with the cam follower 108a of the cam barrel 108. Upon application of a rotating force by an unillustrated driving portion, the cam barrel 108 moves in the optical axis direction while rotating around the optical axis in accordance with the cam track of the fixed barrel 107.
Reference Numeral 109 denotes a rectilinear barrel, which is rotatably engaged to the inner peripheral surface of the cam barrel 108. Reference Numeral 109a denotes a claw-shaped portion, which prevents the falling off of the rectilinear barrel 109 from the cam barrel 108. Reference Numeral 109b denotes a protrusion, extending in the radial direction of the lens apparatus from the rectilinear barrel 109. Reference numeral 107a denotes a rectilinear groove portion, which is formed in the inner peripheral surface of the fixed barrel 107 so as to extend in the optical axis direction. By the engagement action of the protrusion 109b and the rectilinear groove portion 107a, the rectilinear barrel 109 moves in the optical axis direction without rotating around the optical axis in accordance with the rotation operation of the cam barrel 108.
Reference Numeral 110 denotes a first lens unit holding barrel, which holds the first lens unit 104. Reference Numeral 110a denotes a first cam follower, which is fixed to the first lens unit holding barrel 110. The first cam follower 110a moves along the cam track of a first cam that is formed in the inner peripheral surface of the cam barrel 108. Reference Numeral 111 denotes a second lens unit holding barrel, which holds the second lens unit 105. As with the first lens unit holding barrel 110, the second lens unit holding barrel 111 is provided with a second cam follower, which protrudes outward in the radial direction. And the second cam follower moves along the track of a second cam formed in the inner peripheral surface of the cam barrel 108.
Furthermore, in the rectilinear barrel 109, an opening that extends in the optical axis direction is formed, and by the opening engaging with the first cam follower, the first lens unit holding barrel 110 moves rectilinearly. And the first lens unit holding barrel 110 moves, without rotating, in the optical axis direction along the first cam formed in the inner side of the cam barrel 108 in accordance with the rotation operation of the cam barrel 108. By the above arrangement, the first and second lens unit holding barrels 110 and 111 can be moved from the housing region to the image taking region.
Reference Numeral 112 denotes a third lens unit holding barrel, which holds the third lens unit 106. The third lens unit 106 is a lens unit for focusing, and the focusing operation is enabled by moving the third lens unit holding barrel 112 in the optical axis direction.
Reference Numeral 113 denotes a guide rod, which is fixed to the CCD mounting base plate 102 and supports the third lens unit holding barrel 112 in a manner enabling movement along the optical axis. Reference Numeral 114a denotes a screw, which rotates upon receiving a driving force from a motor 114. Reference Numeral 115a denotes a bearing of the guide rod 113 and 115b denotes a bearing, which supports the front end of the screw 114a. The bearings 115a and 115b are fixed to the CCD mounting base plate 102. A nut, which engages with the screw 114a, is supported in an unrotatable manner on the third lens unit holding barrel 112, and the third lens unit holding barrel 112 is thereby enabled to be moved in the optical axis direction by the motor 114 to perform the focusing operation.
With such an image taking apparatus having a housing region for housing a lens apparatus, portability and compact housing features are required in particular, and to be specific, the lens apparatus must be made compact in the radial direction and the total length of the lens apparatus in the collapsed state must be made as short as possible.
Thus there are cases where, in the collapsed state, the second lens unit holding barrel 111 is housed upon entering the range of movement of the third lens unit holding barrel 112 as shown in FIG. 11. With such an arrangement, in order to avoid interference (overlapping) with the guide rod 113, the screw 114a, the bearings 115a and 115b thereof, and other various parts for enabling the movement of the third lens unit holding barrel 112, openings must be provided in parts of the second lens unit holding barrel 111.
FIG. 13 shows the second lens unit holding barrel 111 as viewed from the front. As viewed from the front, the second lens unit holding barrel 111 has openings provided at three locations of its periphery in order to avoid interference (overlapping) with the bearing 115b of the screw 114a, the bearing 115a of the guide rod 113, and a bearing (not shown) for a rotation stopping rod for restraining the rotation of the third lens unit holding barrel 112 around the guide rod 113.
However, since the proportion of the area of the second lens unit holding barrel 111 that is taken up by the openings is large, the holding of the lenses may become unstable due to inadequate strength and lead to degradation of the optical performance. Leakage of light rays may also occur.
Here, leakage of light rays means the phenomenon in which light besides the light flux used for image taking reach the image pickup element. In the conventional lens apparatus, there are cases where light rays, which have become incident at a predetermined angle onto the first lens unit 104, become reflected by the inner peripheral surface of the rectilinear barrel 109 and become incident on the image pickup element 101 without passing through the second lens unit 105. However, since there are large openings in the second lens unit holding barrel 111, leakage of light rays could not be repressed and this represses the making of the lens apparatus compact.
On the other hand, if ribs are provided to increase the strength of the second lens unit holding barrel 111 that has openings, the lens apparatus becomes large. The meaning of designing the second lens unit holding barrel 111 so that it enters the movement range of the third lens unit holding barrel 112 in the collapsed state to enable the making of the lens apparatus compact is thereby lost.
Also, if the component parts of the third lens unit holding barrel 112 are positioned so as to avoid overlapping with the second lens unit holding barrel 111, the lens apparatus may become large in the radial direction.
This invention proposes an optimal positioning of the respective parts inside the lens apparatuses for resolving the above issues, and an object thereof is to realize the making of the lens apparatus compact.